At least two significant eye malfunctions, strabismus (crossed-eye) and amblyopia (lazy eye), involve the phenomenon of suppression, which is a sensory malfunction in which one of the eyes in effect is "blind" although it has the capacity for vision. The vision in the crossed or lazy eye is suppressed so that it does not interfere with the "good" eye. Typically, the suppression in strabismus and amblyopia is constant. In other cases, not involving strabismus or amblyopia, one or both eyes may be suppressed intermittently, which is referred to generally as intermittent central suppression (ICS). ICS occurs at various rates and for various time intervals, typically in the range of 12 to 60 times per minute.
The treatment of constant suppression involves the correction of the crossed or lazy eye so as to make them, in effect, normal in function and appearance, thereby providing the total visual benefit of both eyes (binocular vision). While the effect of constant suppression on vision is known (one eye is in effect blind), the effects of ICS are less well known. Presumably there is some effect on binocular vision. There is also a strong possibility that certain visually mediated functions, in particular reading, are detrimentally affected by ICS. It has been suggested that the intermittent "switching off" of vision in one eye due to ICS results in the intermittent obscuring of the text material being read, so that reading becomes difficult because the same words may look different depending upon whether suppression is present or not, i.e. the timing of the ICS.
While malfunctions such as strabismus and amblyopia are relatively easy to diagnose, the accurate diagnosis of ICS is more difficult. There are a number of tests which have been used for ICS, most of which, however, have proven to be unreliable in the accurate diagnosis of ICS.
One of the traditional treatments used to correct suppression involves the use of binocular devices such as prisms and stereoscopes which in effect force each eye to see a separate portion of a "complete" image. The two partial images are then integrated by the brain to produce a complete image. Each image path can be alternately lighted in order to stimulate each eye separately. Light flashers which impinge directly upon the eye have also been used. However, the significant disadvantage to such a treatment approach is that the treatment can only be accomplished in a practitioner's office, because of the equipment necessary. Such treatment is thus inherently time limited. While improvement in the suppression condition is often possible with such treatment, frequently it is relatively slow and not reliable.
Another common technique for treatment of suppression is patching of the suppressed eye. While typically an effective technique, the appearance presented by an eye patch is usually so undesirable that only a small part of the population, i.e. very young children, will wear a patch for an extended period of time. Hence, patching is not perceived to be practical for the general population.
In at least one condition, i.e. strabismus, surgery can be used as a last resort to prevent the eye from crossing. In amblyopia, as in ICS, however, there is no real need for surgery, and thus the individual with those conditions is left to tolerating either the lack of true binocular vision, in the case of amblyopia, or the disadvantages of intermittent suppression, such as reading difficulties and intermittent loss of binocular vision.
Hence, there is a demonstrated need, longstanding in the art, for an effective and reliable treatment for the suppression phenomenon, both constant and for ICS, as well as more recently, a need to accurately diagnose the existence of intermittent central suppression (ICS).